The present application is concerned with a coding scheme for spectral coefficients of a spectrum of an audio signal usable in, for example, various transform-based audio codecs.
The context-based arithmetic coding is an efficient way of noiselessly encoding the spectral coefficients of a transform-based coder [1]. The context exploits the mutual information between a spectral coefficient and the already coded coefficients lying in its neighborhood. The context is available at both the encoder and decoder side and doesn't need any extra information to be transmitted. In this way, context-based entropy coding has the potential to provide higher gain over memoryless entropy coding. However in practice, the design of the context is seriously constrained due to amongst of others, the memory requirements, the computational complexity and the robustness to channel errors. These constrains limit the efficiency of the context-based entropy coding and engender a lower coding gain especially for tonal signals where the context has to be too limited for exploiting the harmonic structure of the signal.
Moreover, in low delay audio transformed-based coding, low-overlap windows are used to decrease the algorithmic delay. As a direct consequence, the leakage in the MDCT is important for tonal signals and results in a higher quantization noise. The tonal signals can be handled by combining the transform with prediction in frequency domain as it is done for MPEG2/4-AAC [2] or with a prediction in time-domain [3].
It would be favorable to have a coding concept at hand which increases the coding efficiency.